Genetic Diversity

The importance of genetic diversity within a breed has been brought to the forefront as our understanding of genetics increases. To keep a breed healthy and thriving a wide gene pool is essential as without it ‘inbreeding depression’ may occur – small litters, puppies which do not thrive, lack of maternal instinct – these are just a few of the potential problems.

In an effort to address the situation, the Kennel Club Genetics Centre at The Animal Health Trust has commissioned a population analysis of all KC breeds, starting with the Vulnerable Native Breeds of which the Lancashire Heeler is one. It is based on KC registered LHs from 1980-2009 and contains all those on the original Lancashire Heeler Club register which means that virtually all registered dogs up to that date are included.

Population analysis of the Lancashire Heeler breed

Written by Dr Tom Lewis, Animal Health Trust. Reprinted by permission

Genetic analysis of the Kennel Club pedigree records of the UK Lancashire Heeler population has been carried out with the aim of estimating the rate of loss of diversity within the breed and providing guidelines for a future sustainable breeding strategy. The population statistics summarised in the results section provide a picture of the current census size, the number of animals used for breeding, the rate of inbreeding and the estimated effective population size. The observed rate of inbreeding and estimated effective population size indicates the rate at which diversity is being lost within the breed. The analysis also calculates the average relationship (kinship) among all individuals of the breed and this is used to determine the level of inbreeding that might be expected if matings were made among randomly selected dogs from the population (the expected rate of inbreeding). Deviations of the observed inbreeding from expected will reflect processes such as the deliberate mating of closely related individuals (if observed inbreeding is greater than expected) or conversely the introduction of foreign bloodlines (if observed inbreeding is lower than expected).

Summary of results

The analysis was based on the complete computerised pedigree records for the current UK Kennel Club registered Lancashire Heeler population. The rate of inbreeding over the last 30 years (1980-2009) was estimated at 1.98% per generation. This leads to an estimate of an effective population size of 25.4 for the UK Lancashire Heeler population. This is considerably below the recommended minimum effective population size of 100 (maximum inbreeding rate of 0.50% per generation). Comparison of the observed and expected rates of inbreeding show that the observed rate of inbreeding is higher than expected over the last 30 years and this suggests that the mating of close relatives and line-breeding is being practised in this breed (Figure 1). As the breed effective population size is well below the minimum recommended, it is advised that UK Lancashire Heeler breeders should seek to reduce the rate of inbreeding of this breed in the UK.

There is, additionally, evidence for popular sire effects. Figure 2 shows the number of offspring for all Lancashire Heeler sires recorded in the Kennel Club pedigree database. While the majority of sires have 5 or fewer registered offspring, there are 17 sires with 50 or more offspring apiece. The largest number of offspring by a single sire is 128. Some dams are also more prolific than others, 19 dams are recorded as having more than 20 offspring. The maximum number of offspring for a dam is 27.

Some simple adjustments to the breeding strategy would enable the breed to achieve an effective population size approaching the threshold required to reach a sustainable rate of inbreeding (no more than 0.50% per generation). Some recommendations to this end are outlined below.

Recommendations

Reduce the relatedness of individual sires and dams used

The observed rate of inbreeding is largely as a consequence of related individuals being mated. Expanding the practice of breeding from minimally related sires and dams would assist in keeping the rate of inbreeding low. Inbreeding coefficients for prospective matings can be obtained through the Kennel Club's Mate Select toolbox:

Restricting the number of offspring by popular sires will help to increase the total number of sires used. The average number of offspring per sire is around 11 and it is recommended that individual sires should not contribute substantially more offspring than the average. An advanced genetic technique called 'optimum contribution theory' can be used to calculate the precise contribution that each individual dog should make. The KC Genetics Centre is currently researching how this technique could be implemented in dog breeds and what the practical implications might be.

Make use of overseas bloodlines

The importation or use for breeding of unrelated dogs from overseas bloodlines can help with the management of inbreeding, and is to be encouraged. However, breeders should be aware that imported animals bring only limited pedigree information and so the degree of genetic relationship between animals may be under-estimated.

Population Analysis Results

Breed

Lancashire Heeler

*Average no. KC registrations/year

143.9

Estimated census size

1,500

No. sires used/year

28.4

No. dams used/year

44.1

Mean no. dams/sire

1.55

Maximum no. offspring (sire)

128

Maximum no. offspring (dam)

27

Mean no. offspring/sire

11.07

Mean no. offspring/dam

5.81

Generation interval (sire) in years

4.32

Generation interval (dam) in years

3.46

Average inbreeding coefficient

0.077

Average kinship coefficient

0.068

Estimated rate of inbreeding (per year)

0.51%

Estimated rate of inbreeding (per generation)

1.98%

Estimated effective population size (Ne)

25.4

*All statistics are estimated based on dogs born between the years 1980-2009. Inbreeding calculations utilise all recorded pedigree information, including that recorded prior to 1980.

Figure 1. Trend in observed and expected inbreeding since 1980.

Figure 2. Histogram of number of offspring per sire.

Figure 3. Histogram of number of offspring per dam.

Breed Health Correspondent Comment:

As you may have realised, Tom was unaware of the pool of unregistered dogs which we know exists and we corresponded about this. He wrote: ‘Your suggestion of using unregistered Heelers as a way of boosting the genetic diversity is certainly interesting and would I imagine, achieve the aim but we cannot be certain unless we look at the DNA sequence. Because the unregistered dogs are of unrecorded ancestry, we are unable to determine the degree of genetic relationship, which we normally do using pedigree information. We could record the ‘unregistered’ dogs as completely unrelated – which is almost certainly wrong but is the only consistent way to deal with missing information. This in effect, is what we have to do with imported dogs – they bring a certain number of generations of pedigrees with them but beyond that we have to assume those dogs are unrelated. This may result in underestimating the true level of inbreeding. The alternative, as I say, is to determine inbreeding using DNA sequence. This is preferable as you are looking at actual values, rather than estimated relationship derived form pedigree. However, it is expensive at the moment, although it will probably gradually decline in price over time.’